Soybean Yellowing at V2 growth

Soybean Yellowing at V2 growth


My name is Shawn Conley, I’m the state soybean
and small grains Extension specialist at the University of Wisconsin–Madison. Today, what we want to do is discuss some
of the yellowing issues we’ve seen in our early season beans in 2009. What we’ve generally seen, it’s been a
very cool year, compared to the 2008 growing season. We’re about the same for GD use, but over
the last 30 years we’re probably somewhere between 120 units behind. What that’s really done is limited some
of our growth on our soybeans that were even planted earlier. Generally what we’re seeing is a lot of
questions coming in related to yellow soybeans. Now, if we look in this instance, what we
want to do is identify, trying to determine what is causing some of this yellowing. Obviously, a lot of times, what we’ll generally
hear are questions related to glyphosate injury, or the yellow flash with glyphosate. However, as you can see in this field we haven’t
applied any glyphosate to this point, so therefore we know it has nothing to do with chemicals. So again, what we need to think about is in
the physiology of a soybean plant and what’s going on. So, here’s a good example of a soybean plant
where we see the newest trifoliate that is open is very yellow and chlorotic. Okay, this is basically a V2 soybean plant. Now, if we dig up a soybean plant, and what
we really want to do is, it kind of looks like it’s nitrogen stressed, and as we identify
this plant, what we’re looking at is basically the nitrogen coming into this plant and what
it’s cause by. If we look at the cotyledons, we see that
we basically almost utilized all of the nutrients on our cotyledons. Generally, a soybean plant will depend on
the cotyledons until it hits about the B1 growth stage. At that point, these cotyledons are basically
sloughed off, you see how they’re going to be falling off the soybean plant very quickly. So, in between when the cotyledons stop being
a function of the soybean plant, a nodulation occurs. We sometimes see this yellow coloration. If we look here, we split a nodule, it’s
still relatively white inside and what that has indicated to us is that the soybean plant
has not started fixing nitrogen on its own. So, in a sense, what we’ve seen in this
last year is the slower growth, the cotyledons basically are no longer of use to the soybean
plant, the nodulation hasn’t occurred, so we are in a sense, lacking nitrogen in these
V2 soybean plants. However, within the next five days at max,
these soybean plants will begin to actively fix nitrogen and this yellow coloration these
trifoliates will disappear, and growth will remain as usual.